Self Starting Method and an Apparatus for Sensorless Commutation of Brushless CD Motors

Abstract

A method and apparatus for electronic control of a direct current motor is disclosed based upon a sensorless commutation technique using voltage vector analysis. A voltage vector is produced by addition of supply phase voltage vectors of energized windings with the back-electromotive force vector of the unenergized winding. The resultant voltage vector rotates at the same speed as the rotor and possesses rotor position information used to commutate phase windings. The angle that the resultant voltage vector makes with the real axis is measured to commutate the phase windings. By parking the rotor in a predetermined position, this technique can be used to efficiently start the motor from rest and commutate phase windings during normal operation.

1 . A system for operating a brushless DC motor, said system comprising:
 a brushless DC motor;   a processor capable of determining a BEMF Space Vector; and   a processor capable of determining the angle that the BEMF Space Vector makes with the real axis.   
     
     
         2 . The system of  claim 1  wherein the processor capable of determining the BEMF space vector is the same as the processor capable of determining the angle that the BEMF Space Vector makes with the real axis. 
     
     
         3 . The system of  claim 1  wherein the processor capable of determining the BEMF space vector is different from the processor capable of determining the angle that the BEMF Space Vector makes with the real axis. 
     
     
         4 . The system in  claim 1  wherein determination of the BEMF Space Vector is performed by addition of phase voltage vectors of the energized windings and the BEMF vector of the unenergized winding. 
     
     
         5 . The system in  claim 1  further including provisions for disabling angle determination during a commutation interval in which a resultant voltage vector is produced that does not possess rotor position information. 
     
     
         6 . A method of commutating an electric motor comprising rotating the rotor in only a clockwise direction or only an anticlockwise direction. 
     
     
         7 . The method of  claim 6  further comprising determining the position of a rotor of a brushless DC motor. 
     
     
         8 . The method of  claim 6  further comprising summing phase winding voltage vectors of energized windings with the BEMF vector of an unenergized winding to determine a BEMF Space Vector and determining an angle that the BEMF Space Vector makes with the real axis. 
     
     
         9 . The method of  claim 6  further comprising energizing and deenergizing phase windings based on the position of the BEMF space vector. 
     
     
         10 . The method of  claim 6  wherein voltage vectors are determined by projection of detected phase winding voltages along the phase winding's magnetic axis. 
     
     
         11 . The method of  claim 6  wherein the angle that the BEMF Space Vector makes with the real axis is determined using the ratio of the real value of the BEMF Space Vector to the imaginary value of the BEMF Space Vector or the inverse ratio thereof. 
     
     
         12 . The method of  claim 6  wherein the motor is a DC motor that includes a plurality of phases and a plurality of poles. 
     
     
         13 . The method of  claim 6  wherein the phase winding voltage vectors are produced by the referral of the scalar phase voltages in electric circuits to magnetic axes in the corresponding magnetic circuits that are a result of the equality of scalar electric and vector magnetic current magnitudes. 
     
     
         14 . The method of  claim 6  wherein the BEMF Space Vector rotates at the same speed as that of the rotor and provides rotor position information determined using the angle that the BEMF Space Vector makes with the real positive axis. 
     
     
         15 . The method of  claim 6  wherein the rotor position information is used to commutate phase windings.